1. Technical Field
This invention relates to the field of deposition tool cleaning. More specifically, the invention relates to a method for cleaning plasma enhanced chemical vapor deposition (PECVD) tools.
2. Background Art
In the electronics industry, various techniques have been developed whereby selected materials, such as, conductors, insulators, or semiconductors, may be deposited on a substrate. For example, such techniques are often used to deposit successive conductive, semi-conductive, or insulative layers on a silicon wafer in the production of an integrated circuit (IC). Generally, deposition techniques result in a film of deposition materials collecting on surfaces other than the target substrate, that is, the deposition materials also collect on the tool surfaces or other equipment used in the deposition process. In many electronic component fabrication processes, a very clean environment is required to produce components of acceptable quality. The film that builds up on the tool or other equipment surfaces may easily degrade cleanliness and lead to defects in the component. Accordingly, it is well accepted that deposition tools or other equipment must be periodically cleaned to remove the unwanted film of deposition materials.
One type of deposition process is chemical vapor deposition (CVD), wherein reactants are introduced as gases into a heated processing chamber. The heat assists reaction of the gaseous components and the resulting reaction product deposits on the desired substrate. As discussed above, the reaction product (deposition material) also deposits on the walls of the chamber and other equipment therein, creating a potentially deleterious film. One subtype of CVD is plasma enhanced CVD (PECVD), wherein a plasma is established in the processing chamber. Exposing the reactants to the plasma increases their reactivity, thus, less heat is required in the chamber to yield the desired deposition.
A generally preferred method of cleaning deposition tools, particularly PECVD tools, involves the use of fluorinated compounds. For example, C.sub.2 F.sub.6, a perfluorinated compound (PFC), is very frequently used. Other PFCs, such as CF.sub.4, C.sub.3 F.sub.8, SF.sub.6, and NF.sub.3 are also used. Essentially, the combination of a plasma and a PFC generates chemically active fluorine species, such as ions and radicals, that react with the film on the chamber walls and other equipment, producing a gaseous product that can then be removed from the tool. Unfortunately, PFCs are have been found to contribute to global warming and C.sub.2 F.sub.6 has a long atmospheric life of more than 10,000 years. Depending on the process, as much as 80% of C.sub.2 F.sub.6 used in a clean can be unreacted and exhausted into the atmosphere. High emissions of other PFCs have been similarly observed. Accordingly, extensive efforts are underway in the semiconductor industry to reduce PFC emissions through replacement with non-PFCs, abatement of excess emissions, etc. For example, destruction or recycling of the unreacted PFCs has been and continues to be explored. Destruction and recycling have been somewhat successful in reducing PFCs without impact on the cleaning process, nevertheless, such options require significant and costly modifications to existing tools or other equipment.
One problem with such efforts is that they concentrate on reducing emissions without any significant change in the various cleaning methods currently used. By contrast, what is needed is a fundamental change in current cleaning methods specifically for the purpose of reducing emissions. Fundamental changes in cleaning methods have been proposed in the past, however, the purpose of such changes has been to improve cleaning ability, not to reduce PFC emissions. For example, PFCs have been combined with other gases in attempts to improve cleaning ability. NF.sub.3 /O.sub.2 cleans were once used to clean CVD tools, but they yielded overly reactive conditions, producing excessive wear on the tools, inconsistent cleaning of the tools, and problems with foreign material in components fabricated using the cleaned tools. Also, NF.sub.3 /Ar cleans have been attempted with similar problems due partly to sputtering of the argon. Since previous fundamental changes concentrated on improving cleaning ability, it is no surprise that they have not produced the needed reduction in emissions.
Thus, it can be seen from the above discussion that it would be an improvement in the art to provide a fundamentally changed method for cleaning deposition tools, particularly CVD tools, that reduces PFC emissions. To be clearly suitable as a replacement for existing cleaning methods, such method should offer comparable cleaning ability without impacting fabrication of components and incurring excessive costs.